Lithographic printing



LITHOGRAPHIC PRINTING William H. Wood, Mantna, and Dolor N. Adams, Independence, Ohio, assignors to Harris-Intertype Corporation, llleveland, Ohio, a corporation of Delaware No Drawing. Application December 15, 1955 Serial No. 553,209

21 Claims. (Cl. 101-1492) The present invention, relating as indicated to lithographic printing, has more particular regard to lithographic plate treating materials and to methods of using the same. One such particular use is as a treating medium suitable for dampening lithographic plates during printing, a solution for such use being also known as a fountain solution. The material may also be used in the preliminary plate cleaning operation known as counteretching; for pre-etching preparatory to coating a plate with a light sensitized colloidal solution; or for dc-sensitizing the non-image areas of the plate after development of the image.

One of the principal disadvantages of solutions heretofore generally used for the foregoing operations in lithographic printing is that they have contained chromium compounds which produce chromium poisoning in the case of many operators working with such materials. Some attempts have been made to produce treating solutions containing no chromium but such have been only partially successful and as a result the chromium-containing solutions are still widely used.

Accordingly the principal object of the present invention is to provide a new and advantageous plate treatment and in particular, one which omits chromium. Other objects and advantages of the invention will appear from the following description.

To the accomplishment of the foregoing and related ends, said invention, then, comprises the steps and ingredients hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

in accordance with the invention a lithographic plate is subjected to the action of a treating-liquid which includes an agent of the class consisting of water-soluble perhalogenated, aliphatic saturated fatty acids and their water-soluble salts. Perfluoro and perchloro-acetic and propionic acids are examples of such compounds, particularly satisfactory results having been obtained with the use of trifluoro-acetic acid, CF CO H, and of trichloro-acetic acid, CCl CO H, as in the several specific examples or formulas for etching, de-sensitizing, dampening and other compositions hereinafter set forth.

It is significant that in all such compositions no chrmium compound is required; nevertheless superior results in operation are obtained. At the same time, the relationship of acidity (degree of ionization) to concentration is in the range desirable in lithography; the anion is only slightly corrosive to the metals such as zinc and aluminum, ordinarily used in lithography; there is a solvent action on colloids used in sensitizing lithographic plates; there is absence of harmful effects upon the usual inks, driers and other materials used in lithography.

This treatment may be used at any of the appropriate steps in lithographic plate making and handling, such rates Patent i Trifluoro-acetic acid 45.0

' Sodium hemibasic phosphate 65.0

Urea l6.0 Nitric acid (Sp. gr. l-42) a- 25.5

ice

for instance being dampening, counteretching, pre-etching and desensitizing.

While acids of the class mentioned above are in general useful in this connection, as already noted the trihalogen acetic and propionic acids are preferred, and still more definitely it is preferred to employ tri-fiuoroacetic acid or tri-chloro-acetic acid. With such acid, a water-soluble thiourea inhibitor is employed, preferably one from the group consisting of thiourea, ethylene thiourea and 13 dimethyl thiourea. Of these, thiourea is preferred. An agent providing in solution a phosphate ion or nitrate ion is included, and preferably both ions are present. It is also desirable to use a small amount of a Water-soluble gum of the type generally used in lithographic dampening solutions, such as gum arabic.

By properly selecting the foregoing ingredients, a liquid concentrate may be prepared which may then be diluted for use as a fountain solution on the press, or may be diluted to a lesser extent and used as a pre-etch or desensitizing etch. Using other selected ingredients, a dry solid formulation may be made which, when dissolved in water and diluted to the proper extent may be used for the above purposes.

In illustration, the following examples are given of the use of trifiuoro-acetic acid in various combinations and in various solutions employed in lithographic printing,

1. Counter-etch. Water, and tritiuoro-acetic acid in amount of l to 10 percent. Maximum is imposed by practical considerations.

II. Counter-etch and pre-etch combined. Water, and

trifluoro-acetic acid 1 to 20 percent. And an equal volume of a gum solution, e. g. gum arabic, of 1 to 25 percent concentration.

IlI. Desensitizing etch. The solution of Example II may be used for this operation. Or, a composition comprising trifiuoro-acetic acid up to 0.65 lb. maximum, sodium hemibasic phosphate 2 lbs, and tannic acid 1 lb., per gallon of water.

IV. Dampening solution. Water, with tritluoro-acetic acid 1 to 10 percent, and the pH adjusted to 3 to 6 depending upon the particular plate metal, the inks, etc. Suitable bases for adjustment of the pH are sodium hydroxide, potassium hydroxide, ammonium hydroxide. Use /2 to 2 oz. of the concentrated solution per gallon of water on the press.

V. Dampening solution. Equal parts by volume of tritluoro-acetic acid 1 to 10 percent, and gum arabic solution, the gum being in 15 to 25 percent concentration, and the pH being adjusted to afore-mentioned range by a hydroxide of sodium, potassium or ammonium, or by a suitable alkaline salt, such as a phosphate. This is used 1 to 4 oz. of solution per gallon of water on the press.

VI. Dampening solution. A solution formulated to take into account performance of a water system as a whole was made of the following ingredients added to one liter of water, viz.:

VII. Dampening solution. An alternative formula for the stock solution or concentrate given in the preceding paragraph may be made by adding to one liter of water the following, viz.:

Trifluoro-acetic acid ml 30.0 Sodium hemibasic-phosphate g 64.7 Urea nitrate g 32.0 Thiourea g 92.0

In using the foregoing stock solution for printing with black ink, 1 02. thereof with the addition of oz. of 14 B. gum arabic solution to the gallon, gives satisfactory results, such solution having a pH concentration of 2.5. Likewise, satisfactory results have been obtained for printing with blue and colored inks, using /2 oz. thereof with the addition of oz. of B. gum arabic solution to the gallon, the resulting solution having a pH concentration of 4.3.

VIII. Dampening solution. The following is a formu lation corresponding in general with Examples VI and VII, but in which trichloro-acetic acid has been substituted for trifluoro-acetic acid, viz.:

Lb. Trichloro-acetic acid 1.0 Sodium hemibasic phosphate 1.0 Urea nitrate 0.5 Thiourea 1.4

The concentrate formed by adding the foregoing to 1.86 gal. of water, when used at the rate of 1 oz. per gallon of additional water, plus /4 oz. of gum as in preceding example, gave satisfactory result as dampening solution when printing with black ink; so, too, at the rate of /2 oz. plus /s oz. of gum, when printing with blue ink; the pH of the dampening solution being adjusted to 3.4, preferably by adding ammonia.

Since trichloro-acetic acid is a solid, the above listed ingredients have the advantage that they may be mixed and packaged in dry form, or made up in the form of a concentrated solution, as preferred. In either case, just as in preceding example, phenol will desirably be added as a preservative at the rate of 0.14 lb. to the dry ingredients or of 0.16 lb. of 88% phenol solution to a concentrate made as set forth.

Certain of the foregoing solutions, particularly those prepared in accordance with Examples VII and VIII have been found to run successively not only with a variety of colored inks, but on either zinc or aluminum plates made by the known surface or deep-etch processes, as well as on so-called pre-sensitized or diazo-type plates. When used to run zinc plates, the water vibrator roll will desirably be chrome plated.

Also, where, as in certain of the foregoing examples, gum arabic is included in or added to the treating solution, a small percent of phenol (e. g. 1 g. in the case of Example VIII) will also desirably be included in order to increase the keeping quality of the solution.

A ratio of from 0.2 to 0.4 mol of acid per liter of concentrate has been found satisfactory for use in the several dampening solutions illustrated by the foregoing examples or formulas, in the case of both trifluoro-acetic acid and trichloro-acetic acid. Similarly, the employment of water-soluble thicurea in the mol ratio of about 3 of inhibitor to 1 of acid is recommended. In each case the concentrate, as such, or diluted to a less extent than where intended foruse as a dampening solution, has also been found satisfactory for pre-etching as well as for desensitizing plates.

The nitrate ingredient in the several examples or formulas given above is particularly desirable in treating aluminum lithographic plates; while the hemibasic phosphate is particularly desirable in treating zinc plates. However, these two ingredients are compatible with each other and accordingly, as in Example VIII, both are included so that the resulting concentrate or solution may be satisfactorily used with either zinc or aluminum plates. Inclusion of the phosphate is also desirable because it counteracts any hardness encounted in the water employed in making up the working solution.

It is to be understood that the use of compositions such as disclosed herein, particularly in the form of a dampening solution, is not limited to metal lithographic plates, but may be effective in the case of paper-back or other kinds of plates. Furthermore, by the phrase preparing a lithographic plate for printing as used in the following claims, it is intended to connote any of plate treating steps hcreinbefore described.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the process herein disclosed or the materials employed in carrying out the process, provided the steps or materials stated by any of the following claims or the equivalent thereof be employed.

We therefore particularly point out and distinctly claim as our invention:

l. In a method of preparing a lithographic plate for printing, the step which consists in applying to the printing surface of such plate a solution consisting essentially of water and a relatively small percent of an agent from the class consisting of water-soluble per-halogenated aliphatic saturated fatty acids and their water-soluble salts and having an acid pH.

2. In a method of preparing a lithographic plate for printing, the step which consists in applying to the printing surface of such plate a solution consisting essentially of water and a relatively small percent of an agent from the class consisting of per-halogenated acetic and propionic acids and their water-soluble salts and having an acid pH.

3. In a method of preparing a lithographic plate for printing, the step which consists in applying to the printing surface of such plate a water solution consisting essentially of a relatively small percent of an agent from the class consisting of per-halogenated acetic and propionic acids and their water-soluble salts together with a corre sponding small percent of a chromium-free agent providing an ion of the class consisting of phosphate and nitrate ions, said solution having an acid pH.

4. In a method of preparing a lithographic plate for printing, the step which consists in applying to the printing surface of such plate a water solution consisting essentially of a relatively small percent of an agent from the class consisting of per-halogenated acetic and propionic acids and their water-soluble salts together with a corresponding small percent of a water-soluble thiourea and having an acid pH.

5. In a method of preparing a lithographic plate for printing, the step which consists in applying to the printing surface of such plate a water solution having an acid pH and consisting essentially of a relatively small percent of an agent from the class consisting of per-halogenated acetic and propionic acids and their water-solu- 'ble salts together with a corresponding small percent each of a phosphate ion-providing agent, a nitrate ion-providing agent and a water soluble thiourea, said agents being free of chromium.

6. In a method of preparing a lithographic plate for printing, the step which consists in applying to the printing surface of such plate a water solution consisting essentially of from 1 to 10 percent of trifluoro-acetic acid and a corresponding small percent each of a phosphate ion-providing agent, a nitrate ionproviding agent and a water-soluble thiourea, said agents being free of chromium.

7. In a method of preparing a lithographic plate for printing, the step which consists in applying to the printing surface of such plate a water solution consisting essentially of from 1 to 10 percent of trichloro-acetic acid and a corresponding small percent each of a phosphate ion-providing agent, a nitrate ion-providing agent and a water-soluble thiourea, said agents being free of chromium.

8. A new composition of matter for use when dissolved in Water as a medium having an acid pH for treating lithographic plates, such composition consisting essentially of a fatty acid material selected from the group consisting of a water-soluble per-halogenated aliphatic saturated fatty acid and its water-soluble salts, and a Water-soluble thiourea inhibitor.

9. A new composition of matter for use when dissolved in water as a medium having an acid pH for treating lithographic plates, such composition consisting essentially of a fatty acid material selected from the group consisting of a water-soluble per-halogenated aliphatic saturated fatty acid and its water-soluble salts, and a chromium-free agent providing an ion of the class consisting of phosphate and nitrate ions.

10. A new composition of matter for use when dissolved in water as a medium having an acid pH for treating lithographic plates, such composition consisting essentially of a fatty acid material selected from the group consisting of a water-soluble per-halogenated aliphatic saturated fatty acid and its water-soluble salts, a watersoluble thiourea inhibitor, and a chromium-free agent providing an ion of the class consisting of phosphate and nitrate ions.

11. A new composition of matter for use when dissolved in water as a medium for treating lithographic plates in order to prepare same for printing, such composition consisting essentially of a water-soluble perhalogenated aliphatic saturated fatty acid of the class consisting of tIi-halogenated acetic and propionic acid, a water-soluble thiourea inhibitor, and a chromium-free agent providing an ion of the class consisting of phosphate and nitrate ions.

12. A new composition of matter for use when dissolved in water as a medium for treating lithographic plates in order to prepare same for printing, such composition consisting essentially of a water-soluble perhalogenated aliphatic saturated fatty acid, a water-soluble thiourea of the class consisting of thiourea, ethylene thiourea and 1-3 dimethyl thiourea.

13. A new composition of matter for use when dissolved in water as a medium for treating lithographic plates in order to prepare same for printing, such composition consisting essentially of trifiuoro-acetic acid, sodium hemibasic phosphate, urea nitrate and thiourea.

14. A new composition of matter for use when dissolved in water as a medium for treating lithographic plates in order to prepare same for printing, such composition consisting essentially of trichloro-acetic acid, sodium hemibasic phosphate, urea nitrate and .thiourea.

15. A new composition of matter for use when dissolved in water as a medium for treating lithographic plates in order to prepare same for printing, such composition consisting essentially of approximately equal parts by weight of trichloro-acetic acid and sodium hemibasic phosphate, one-half part of urea nitrate and one and one-half parts of thiourea.

16. A water solution of the composition defined in claim 8, such solution having added thereto a relatively small percent of a hydrophillic colloid.

17. A water solution of the composition defined in claim 8, such solution having added thereto a relatively small percent of gum arabic.

18. A water solution of the composition defined in claim 8, such solution having added thereto a relatively small percent each of gum arabic and of phenol.

19. A water solution of the composition defined in claim 9, such a solution having added thereto a relatively small percent of a hydrophillic colloid.

20. A water solution of the composition defined in claim 9, such solution having added thereto a relatively 7 small percent of gum arabic.

References Cited in the file of this patent UNITED STATES PATENTS Rowell Oct. 23, 1934 Dell Jan. 21, 1941 o Fe 1941 

1. IN A METHOD OF PREPARING A LITHOGRAPHIC PLATE FOR PRINTING, THE STEP WHICH CONSISTS IN APPLYING TO THE PRINTING SURFACE OF SUCH PLATE A SOLUTION CONSISTING ESSENTIALLY OF WATER AND A RELATIVELY SMALL PERCENT OF AN AGENT FROM THE CLASS CONSISTING OF WATER-SOLUBLE PER-HALOGENATED ALIPHATIC SATURATED FATTY ACIDS AND THEIR WATER-SOLUBLE SALTS AND HAVING AN ACID PH. 